1. Field of the Invention
The present invention relates to implantable medical stimulators and more particularly to medical leads having a plurality of electrode contacts.
2. Description of the Related Art
Electrical stimulation of electrically excitable tissue such as the brain and/or nerve tissue of the spinal cord can result in pain reduction and/or elimination for the living organism having the stimulated electrically excitable tissue. Thus, for example, medical leads having electrode contacts have been implanted near the spinal column of the human body to provide pain relief for the chronic intractable pain.
Medical leads, which comprise electrode contacts and lead bodies, have been developed to conduct electrical stimulation signals from implantable pulse generators to targeted nerve fibers. These medical leads may be percutaneous leads with the electrode contacts spaced along the lead body. Also, the medical leads may be surgical leads with electrode contacts spaced in an array on a lead paddle. A percutaneously insertable medical lead within a human for applying electrical stimulation to the spinal cord is discussed in U.S. Pat. No. 4,044,774 issued to Corbin et al., and herein is incorporated by reference.
Historically, a straight wire lead body had been used between a medical lead paddle having the electrode contacts and the implantable pulse generator, both of which have been anchored to surrounding tissue. Problems arose using straight wire lead bodies because the straight wire is inelastic and has shorter flex life. As a result of this inelasticity and more limited flex life, when a patient with an implanted medical stimulator and medical lead moves or bends, a straight wire lead body becomes taut and pulls on or places a load on the electrode contacts or the pulse generator or both. Specifically, patient movement tugs or pulls on the wire connection to the electrode contacts of the lead paddle or the wire connection to the implantable pulse generator or both. One solution to this problem has been to coil the wire conductors in the lead body so that the lead body stretches or flexes when the patient moves or shifts around. However, the coiled wire in the lead body disadvantageously increases electrical resistance, sometimes up to three times the electrical resistance in a straight wire lead body. Moreover, when multiple coiled wire conductors are used in a lead body, the pitch angle of the wire conductors decreases, thus disadvantageously resulting in flatter pitch and reduced flex life. In response to this problem with flex life, straight miniature cables were used as wire conductors. However, while the flex life of the wire conductors improved with miniature cables, problems again arose with the straight miniature cable pulling or tugging at the connection between the cable and the electrode contact, and the connection between the cable and the pulse generator. A solution to these problems is disclosed in the present invention.